This invention is directed to a means for locking a pipeline plug in a pipeline flange.
When a section of a pipeline must be repaired or modified, a temporary bypass pipeline, with temporary valves, is usually installed to circumvent the section. T-fittings are mounted on the main pipeline, one on each side of the section in question, and the bypass pipeline is attached to flanges on the T-fittings. Each end of the section may then be plugged, and repairs may be made, the bypass pipeline allowing fuel flow to continue uninterrupted.
Once work on the section is complete, it is desirable to remove the bypass pipeline and temporary valves for use elsewhere, and then to plug the flanges. Cylindrically shaped plugs may be inserted into the flanges and locked in place, preventing loss of fluid from the pipeline through the flanges.
One means of locking a plug in place in a flange is to provide the plug with an annular groove which is engaged by a plug locking means that is carried within the flange. Such a locking means may comprise either arcuate locking collars or unthreaded pins which are carried within the flange on threaded pins, the threaded pins being used to insert the collars or unthreaded pins into--and retract then from--the annular groove, for locking and unlocking the plug, respectively.
One device using plug locking means carried on threaded pins is described in Ver Nooy U.S. Pat. No. 2,988,111. This device utilizes threaded pins with unthreaded portions at one end thereof, which engage an annular groove on the plug for locking the plug in place. A disadvantage of this device is that the unthreaded portion of each pin is relatively narrow in cross-section, leading to the exertion of high pressure by the plug on the pin due to the force of the fluid in the pipeline upon the plug, thus leading to a greater likelihood of damage to both the pin and the plug.
A device utilizing locking collars to lock a flange plug in place is disclosed in Ver Nooy U.S. Pat. No. 2,771,096. In that device, a threaded pin carrying an arcuate locking collar is mounted in a threaded inner cylindrical bore, the pin including a portion that extends into a outer cylindrical bore. The threaded pin is rotated for insertion and retraction of the collar into and out of the plug's annular groove. The inner cylindrical bore in Ver Nooy U.S. Pat. No. 2,771,096 must be coaxial with the outer cylindrical bore within very close tolerances, to prevent the pin from binding against one of the bores upon being rotated.
Another device using a locking collar concept is disclosed in Publication No. 00-3795-0079 and Bulletin 504.0 of T. D. Williamson, Inc. of Tulsa, Okla. This device, like Ver Nooy U.S. Pat. No. 2,771,096, relies upon the precise coaxialness of two adjacent cylindrical bores so as to prevent binding of the segment screw (the equivalent of the aforementioned threaded pin) against its associated cylindrical bore. The nut in Williamson carries the retainer ring segment (the equivalent in the Williamson device to the locking collar in Ver Nooy U.S. Pat. No. 2,771,096). Another problem with the Williamson device is that if a worker rotates the segment screw inwardly before the plug is in place, it is possible for the ring segment to fall, or be shaken loose by vibrations, from the segment nut and into the main pipeline, because the ring segment (i.e., locking collar) is not securely attached to the segment nut. In fact, a careless worker could accidentally allow the entire segment nut to be vibrated loose and fall in the same manner, merely by rotating the segment screw (threaded pin) too far and disengaging the screw from the nut. Such a happenstance would require installation of yet another pipeline plug upstream of the flange for repairing the plug locking device; and any parts that fell into the main pipeline would be swept away by the force of the fluid flow.
It is therefore an object of this invention to provide a system for locking a pipeline plug in a pipeline flange wherein locking means for locking the plug in place engages the plug in a relatively large cross-section for preventing damage to either the plug or locking means.
It is another object of this invention to provide a system for locking a pipeline plug in a pipeline flange utilizing a threaded means for locking and unlocking the plug that does not depend upon precise coaxialness of bores in the flange.
It is a further object of this invention to provide a system for locking a pipeline plug in a pipeline flange wherein deviations from manufacturing precision will not result in binding of the components of the system.
It is yet another object of this invention to provide a system for locking a pipeline plug in a pipeline flange wherein the components thereof are securely attached to one another, so that they cannot accidentally become separated during use.
It is a further object of this invention to provide a system for plugging a pipeline flange wherein the components thereof cannot become dislodged or fall into the pipeline, avoiding costly and time-consuming repairs.
Other objects, advantages, features and results will more fully appear in the course of the following description.